As exemplified in Patent Literatures 1 to 2 and Non Patent Literatures 1 to 3 below, techniques to recognize characters present in the three-dimensional space such as a advertising sign from a scene image have been known. In these techniques, the accuracy of recognition is enhanced using external data such as word knowledge and position information of an image-taking location in order to address problems specific to scene images such as variations of light and shade and distortion of characters.
For example, Patent Literature 1 discloses a technique that checks a character string extracted from an advertising sign or the like in an image against a telephone directory database and determines the degree of matching with advertiser data or telephone number data contained in the telephone directory database to thereby determine whether the extracted character string is relevant to an advertiser.
Further, Patent Literature 2 discloses a technique that identifies the position and direction of an image-taking location using a position information acquisition means and a direction information acquisition means included in a character recognition device, checks the identified position and direction against a map database and uses the matched shop name or place name information as word knowledge to thereby enhance the accuracy of recognition.
Furthermore, a Weighted Finite State Transducer (WFST) that represents a set of symbol string transformation and weights as a state transition is used as a technique with a high-speed, high versatility and high expandability in the field of speech recognition and language processing. In relation to the WFST, in the field of character recognition, a technique of acquiring results of character recognition that assumes the acquisition of a character string on a word-by-word basis in word-segmented language such as English is proposed, as exemplified in Non Patent Literature 1 and Non Patent Literature 2. Further, in Non Patent Literature 3, a technique that makes error corrections using the WFST after outputting character recognition results in Japanese is proposed.